All changes to the codebase can be audited and reviewed via GitHub pull requests and commit histories.
Server logs are stored on EBS storage so that they persist even if a server is terminated. These are also accessible via the AWS Cloudwatch service and are kept for a default retention period of 35 days.
Email logs are stored on Postmark and are kept for 45 days.
We keep a record of any critical support incidents for at least 7 years.